Answer-back device for machine switching printing telegraph exchange systems



Aug. 3, 1937. F. s. KINKEAD 2,088,750

ANSWER BACK DEVICE FOR MACHINE SWITCHING PRINTING TELEGRAPH EXCHANGE SYSTEMS Filed Jan. 18, 1956 5 Sheets-Sheet l LARIZED g s Q) I a 3 l3 0 a m v n 6 6 i N Ji" 6 I I k M F ii I l -g. g

E "5 5 r wg 3 INVENTOR FSK/N/(EAD A 7' TOP/VEV Au'g- 1937. F. s KINKEAD 2,088,750

ANSWER BACK DEVICE FOR MACHINE SWITCHING PRINTING TELEGRAPH EXCHANGE SYSTEMS //v VEN 70/? F S. K/N/(EAD A 7'TORNEV Patented Aug. 3, 1937 UNITED STATES ANSWER-BACK DEVICE FOR MACHINE SWITCHING PRINTING TELEGRAPH EX- CHANGE SYSTEMS Fullerton s. Kinkead, Ridgefield Park, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application January 18, 1936, Serial No. 59,679

9 Claims.

-l change system of the identity of the station which is after selection connected to the calling subscribers line. 1

Another object is to apprise a calling subscribe that connection has been established to the correct called station.

Answer-back devices appear to be divided into two classes, namely, those that may be located at thesubscribers station andare usually made a part of the printer, and those that are located at the central oifice. U. S. Patent 1,909,838 granted to C. C. Lane on May 16, 1933, discloses a type of device that forms a part of the printer. at the subscribers station, and U. S. Patent 1,936,200 granted to G. A..Locke and C. C. Lane on Novemher 21, 1933, represents a type that is located at -the.central office.

The present invention belongs to that group of answering devices which are employed as part of the apparatus at the central office. This apparatus may be used with a manually operated switchboard or automatic switching exchange. Preferably, it is adapted to a teletypewriter exchange system employing automatically operated line finder and hunting connector switches of the step-by-step type. Such a system is disclosed in U. S. Patent 1,958,930 granted to- F. J. Singer on May 15, 1934. The answer-back device in this invention is designed to transmit signals identifying the called station as soon as a connection between a calling and a called teletypewriter station has been completed and the printer motor at the called station has started. A special type of line finder switch for each group of one hundred subscribers lines is provided in addition to the line finder switches required for the establishment of connections between subscribers lines. This special line finder switch comprises four banks of one hundred contact terminals each. Cooperating with the special line finder switch is a singlemovement rotary switch having two contact banks and serving as a timing switch for establishing in a predetermined sequence, circuits whereover groups of code signals corresponding to the called stations number are transmitted to the line connection established between two subscriber or teletypewriter stations. The code signals are transmitted by a series of discs fixedly mounted on a continuously rotating shaft and respectively arranged in engaging relation with a series of brushes which effect, during each revolution of the shaft, a predetermined series of openings and closings ofv each of the timing switch circuits. The special line finder switch extends through its bank of terminals the circuits completed in a predetermined sequence by the timing switch. The single-movement rotary switch is individual to the special line finder switch and the disc set is common to all the special line finder switches that may be employed in the system. If the frequency of calls requires it, additional special line finders and their associated timing selectors may be added to serve the same one hundred subscriber lines.

Other objects and features will be found in the following detailed description and accompanying drawings, in which Figs. 1 to 4, inclusive, when placed together as indicated in Figs. 5 and 5A, illustratecircuits and apparatus for automatically sending back to the calling sub- I scriber the code number of the selected called subscriber.

Fig. 1 shows a teletype printer subscriber station A, together with its associated line equipment at the central ofilce and includes all the necessary equipment for receiving and sending printed messages.

Fig. 2 shows a line finder and connector switch circuit of the usual type indicated in squares LF and ON, respectively. The latter is shown connected tothe central ofiice end of a called subscriber line, as indicated at line B, and is capable of being extended to the called subscriber printer station B over conductors 2M and 202.

In Fig. 3 there is represented in schematic form a complete circuit diagram of an identification line finder of the step-by-step type used for finding a called station line circuit when that station has just been put in connection for sending and receiving messages. Said line 'finder, together With a selecting switch of Fig. 3A, serves to identify the number of the called static-n to the calling subscriber.

Fig. 4 shows a common signal distributor for all identification line finders in the olfice. Likewise, there is indicated at Fig. 4A, group relays 401, 405 and 4 l 0 for starting the nearest line finder, there being one for each of ten sub-groups of ten subscriber lines. Identification line finders ILFI, ILFIA and ILFIUA similar to the one shown in Fig. 3, are indicated in Fig. 4B in order to bring out the manner in which these line finders are started. The circuit and apparatus shown in Fig. 4C represents supervisory and alarm equipment usually provided with line finders of this type.

In Fig. 1 of the drawings, there is shown the apparatus and circuit connections for a typical printing telegraph station, such as STA. A, it

being understood that other stations, such as indicated as STA. B of Fig. 2, are similarly equipped. Station A is connected with the central office by means of tip conductor IOI and ring conductor I02, and STA. B is similarly connected over tip conductor 20I and ring conductor 202. At the central office, the line conductors IOI and I02 of station A, which is shown herein as the calling station, are connected to the line finder switch bank 226 of Fig. 2 Other stations in the system are similarly connected by means of conductor.-

pairs to other terminals in said bank. The line finder switch indicated as LF of Fig. 2 is of the step-by-step type described in US. Patent 815,176 granted to A. E. Keith et al. on March 13, 1906.

The subscriber station lines may be arranged in one or more groups of one hundred lines each, and each group may be arranged in ten subgroups of ten lines each. The connector switch designated as CN in Fig. 2 is shown for the purpose of indicating how a calling subscriber, such as STA. A, may by automatic means be connected to another station, such as the called STA. B. If it is desired to trace in detail the establishment of such a connection, reference may be had to- U. S. Patent 1,958,930 granted to F. J. Singer on May 15, 1934.

The features of this invention more particu larly reside in the equipment shown in Figs. 3 and 4 and are effective only after the calling station A has completed dialing the called station B and the printer motor at the called station has started. Under these conditions, the lineequipment for station B in Fig. 2 causes what is termed an identifying line finder shown at'ILFIO in Fig. 3 to find and connect with the line B equipment of Fig. 2, said finders being. similar in most respects to that disclosed and described in the patent to Singer mentioned above. Line finder bank 305 serves to stop the switch on a terminal corresponding to the number of the called line B, all in a manner commonly the part of the usual line finder operation. There'- fore, the three brushes 302, 303 and 304 contacting with the line finder banks 306, 301 and 308 automatically serve to identify the called subscriber station B in a manner later tobe described.

Operationof the system A detailed description will now be given of the manner in which a signal code corresponding to the called station E is automatically transmitted back to the calling subscriber station A.

Calling subscriber A in Fig. 1, prepares to dial subscriber B by first operating key I03 to the right, thus closing an operating circuit for relay I04, extending from ground at back contact and armature relay I05, conductor I06, contact I'I on dial I08, lower back contact and armature relay I09, closed contact IIO of key I03, conductor III, tip'oonductor IOI, conductor II2, left armature and back contact of relay I I3, through winding of start relay I04 to grounded battery. Ground is connected at contact I I4 of key I03 to operate lamp II5 for the purpose of supervising the call.

Start relay I04 operates and closes an obvious circuit for operating relay I I6 which in turn closes a circuit for operating a line finder subgroup relay 203 of Fig. 2, traced from battery through winding relay 203, conductor 204,'right innermost contact of relay IIB to ground at inner left armature and back contact relay II3. Further description of the operation of line finder LF of Fig. 2 may be found in the Singer patent hereinbefore referred to. For the purposes of this description, it may be assumed that line finder LF is accordingly started and eventually the brushes connect with line conductors 205, 206 and 201, shown in Fig. 2. Relays I3I and I32 shown at the bottom of line A equipment serve to cause an identification line finder to find this line under conditions where this line is called by another line but said relays are not effective on originating calls.

A sleeve test circuit is closed upon the brushes contacting with their respective terminals, traced from grounded battery through winding cut-off relay H3 in parallel with grounded battery through resistance Ill and contact II8 on relay II6, thence through contact II9 on relay II6 to conductor 201 and ground, first in the line finder circuit and later in the connector circuit. Cutofi relay II3 operates in this network and locks direct to conductor 20'! at its own right inner contact. A line finder having been started and the line found, it is the function of relay II3 to open the circuit for the line or starting relay I04 to prevent further starting of line finders, all as more particularly described in patents previously mentioned.

Hunting connector In the idle condition of the connector CN of Fig. 2, relay 209 is energized by current normally flowing through its lower winding and its armature is, therefore, held against its back contact. Relay 208 is energized by current normally flowing through its lower winding and its armature is thereby held against its front contact. Negative grounded battery 22! is, however, not connected as indicated by the dotted lines until after the connector has been dialed to the called line.

When the associated line finder finds a line extending to subscriber station A and the cutthrough relay, not shown, in the finder circuit operates, the tip conductor 205 is extended through the finder LF and into the connector circuit through upper winding of polarized relay 208, armature and back contact relay 209 to grounded positive battery. The ring conductor 206 is likewise extended to the line finder and into the connector circuit'through the armature and back contact relay 2I0 to negative battery. As previously traced, line conductors 205 and 206 at this time extend over conductors IN and I02, respectively, and are joined together through relay I09, dial contact I42, and contact I2I of dial key I03 of calling subscriber A. The closure of this circuit causes relay 208 to move its armature to its back contact, thereby operating pulse {relay 2 over a path extending from positive battery 2I2 and armature relay 208 through winding relay 2 to ground. Ground thus connected to front contact 2I3 of pulse relay 2, as is well'known in the operation of step-by-step switching mechanisms, operates a slow release relay for maintaining ground back over conductor 2| 4 to sleeeve 201 for holding the connection and places the connector switch in condition to step vertically and horizontally each time relay 2II releases and reoperates in response to the operation of the subscriber dial. The closure of this circuit also operates relay I09 at station A, thereby causing lamp II5 to be extinguished, indicating to the subscriber that the circuit is cut through and ready for dialing.

Dialing At each interruption of the dial I08. corresponding to the code number of thecalled station B, pulse relay 2 releases due to the deenergization of the upper winding of relay 208, whereby the relay armature is actuated to its associated front contact. As before stated, negative grounded battery 221 is not connected at this time. For further details of the manner in which the connector switch responds to these impulses and the manner in which the cutthrough relay, not shown, functions, reference should be had to patents hereinbefore mentioned. After dialing is completed, the cutthrough relay operates if the called line is idle and causes the polarity on both the calling and called lines to be momentarily reversed.

Starting of motor at station A Reversal of polarity momentarily onthe calling line causes polarized relay I20 at station A to operate and close an obvious operating circuit for the motor start relay I22, which in turn operates and looks through its lower contact to ground through emergency stop key I23 and motor control contact I24 on the station printer. Relay I 22, at its upper contact, closes a circuit for starting printer motor I25 in parallel with four other circuit paths to ground, one for operating relay I05 to permit the closure of the loop circuit through the station transmitter as soon as dialing key I03 is released; the second for operating pulsing polarized relay I26 through its right-hand winding to prevent operation of printer magnet I21 except when a circuit is closed through its left winding; a third path through the lower contact on relay I28 for operating buzzer I29 to inform the subscriber that motor I25 has started; and a fourth path for operating relay I28 to shut off buzzer I29 when the subscriber restores key I03 and momentarily throws it to the left to stop the buzzer signal. The release of key I03 disconnects the dial I08 and lamp II5 from the line and closes the loop circuit through the transmitter I30 and the left winding of relay I26. Current through the left winding of relay I26 overpowers the effect of current in the right winding, causing it to close a circuit at its top contact to the printer magnet I21 for maintaining it in' an operated condition subject to transmitter I30 or to reversalof line battery from the called end of the connection.

Starting 0 motor at station B When the connector circuit connects with the called line B, a relay, such as ZIB, immediately operates and connects ground to brush 2I9, which may then be further traced over conductor 2I1 and through the line cut-off relay 2Z0 winding to battery. Operation of relay 220 extends the tip and ring conductors H5 and 2I6 through to the called subscriber station B, with the winding of relay 22I included in the tip conductor 2I5. As a part of the cut-through operation of the connector previously referred to, a momentary reversal of battery is connected to the called line which causes the motor at station B to start up in identically the same manner as described for the calling station A. That is, a polarized relay at station E corresponding to relay I20 at station A operates and prepares station B for transmitting and receiving messages in the same manner as described'above for station A. The non-locking key corresponding to key I03, however, is in its normal position and the attendant at station B in response to the operation of the buzzer corresponding to buzzer I29 merely operates the key momentarily to the left to stop the buzzer.

Starting identification Zine finder When the connector switch of Fig. 2 makes connection with line B, as above described, the loop to the called station B included relay 22I of an identifying circuit, but this relay did not operate until after the attendant at station 'B operated the key for stopping the buzzer. Relay 22I did not operate on the momentary reversal from the connector because at that time the tip conductor 20I was open at lower front contact of relay corresponding to relay I05 of station A. Relay ZZI operates after a relay similar to relay I20 has locked a relay similar to relay I22 to thereby operate a relay similar to relay I05 after relay 2I0 has been restored to normal. When the attendant at calling station A receives an answer-back signal, he may assume that the attendant at station B is ready to exchange messages with him.

The operation of relay 22I does two things; at its right contact it prepares a battery path through the right winding relay 222 for stopping an identification line finder on the terminal corresponding to the called line; at its left contact it connects ground toleft outer armature and back contact relay 222 which is further traced over conductor 223 and through winding of subgroup.

ILFIO of Fig. 3. The line circuit of station B for.

the purpose of this illustration is thus arbitrarily assumed to be in the tenth level, while station A line circuit is shown connected over leads I33, I34 and I35 and terminating in the first level. Other stations in the system are respectively connected by means of conductor pairs to the other terminal sets in the same line finder switch banks and each line conductor pair is multipled as indicated at 3 I 0 to various levels of other line finder banks in accordance with the well-known slip multiple method disclosed in U. S. Patent 1,161,655 granted to C. L. Goodrum on November 23, 1915.

Subgroup relay 4I0 functions after the usual manner of this form of advance start wire operation to start an idle line finder to hunting for the calling line which, in this case, is a subscriber line that has just been called by another station. Other subgroup relays 40I to 409, inclusive, are represented by relay MI in the first subgroup and relay 405 in intermediate subgroups, each corresponding to a particular group of ten lines. It will be obvious that a detailed description of the operation of the advance start wire circuit is not pertinent to the understanding of this invention, although it may be had by referring to the Goodrum patent, supra. In Fig. 43, however, there are shown relays 4| I, M2 and commutator M3, representing a portion of other ILFI A involved in the start wire circuit and corresponding to relays 3||, 3|2 and commutator -3|3 of the line finder shown in Fig. 3. A detailed description of the functions of this start Wire may be found in the patent to Singer previously re- ILFIDA associated with the same subgroup relay 410. This will serve to stop the finder switch on the tenth level as will later be described. At its upper contact, relay 4|0 closes a circuit for start- :ing the switch tostep to the tenth level. This circuit may be traced from ground on bottom contact relay MS of Fig. 4C over conductor 6 and top contact relay 4), thence over conductor 4|I,

through contact 3|4 on relay 3 of Fig. 3, con- .ductor 3|5 and bottom contact on tenth rotary step springs to battery through winding relay 3 6. Stepping of identification Zine finder The operation of relay 3|6 at its outer lower armature and contact connects ground to conductors 3|'| and 3 H! for controlling the line finder ILFIU. Ground connected to lead 3|l prepares a circuit for stepping the finder on the level in which the terminals of the called line are located. This path may be traced through a normally made contact on the line finder vertical magnet 3|9, conductor 32!] and through the lower winding of relay 3|2, conductor 309 to the brush bearing on commutator bank 3|3. Ground connected to lead 3|8 prepares a path for stopping the line finder on the terminal corresponding to called station line B and is further traced through lower winding relay 32| lower inner contact relay 3|6, conductor 322, back contact 323 on relay 3, lower winding relay 324, conductor 325 to brush 30| which stops the finder switch when the brush finds battery on the terminal 333.

This battery through the right winding relay 222 is placed on terminal 333 over lead 334 by the operation of relay 22| at its right armature and contact.

vGround connected to lead 3|'| also serves to start the line finder to stepping vertically by operating relay 32|. This path is traced from ground on lead 3|! through a break contact on vertical magnet 3|9 and on rotary magnet 326, conductor 321 and through upper winding relay 32| to battery over conductor 328 and top break contact relay 3. Relay 32| at its make contact connects ground that was traced to lead 3|8 from bottom contact on relay 3|6, to armature 329 of relay 3|2 and further traced over its back contact, through winding of vertical magnet 3|9 and conductors 330 and 328 to battery at top contact relay 3. The vertical magnet 3|9 upon operating steps the brush arms of the switch up one level and then due to opening the contact on magnet 3|9 and breaking the operating ground for the top winding relay 32|, previously traced, relay 32| releases, which in turn at its lower armature removes ground from the vertical magnet 3|9. The magnet releases and again closes the associated break contact to again operate relay 32| and in turn the vertical magnet. In

this manner the switch continues to step vertically until the brush of commutator 3|3 comes ing until relay 3 6 releases.

in contact with the terminal 33| whichis grounded by relay 4|0 as traced previously. Upon connecting with this terminal the contact on magnet 3| 9 opens as before but relay 32| does not release because of the presence of ground at commutator terminal 33| which may then be further traced over brush and conductor 309, lowing winding relay 3|2, conductor 320 thence over contact on rotary magnet 326, conductor 321, through top winding relay 32| tobattery on lead 328 at top back contact relay 3| In this manner further stepping of the magnet 3| 9 ceases and due to current flowing through the lower winding of relay 3| 2, the latter operates after a very short time interval and at armature 329 transfers the stepping circuit to the rotary magnet 326 over conductor 332. Said time interval is provided by the slowness of relay 3|2 to operate and prevents any probability of snagging the brushes.

Relay 32| remaining operated .during this transfer of the operating path from the vertical magnet 3|9 to the rotary magnet) 326 at once causes the rotary magnet to be energized and the switch to take one rotary step, whereupon commutator brush breaks its contact with terminal 33| and allows relay 32| to release to open the ground that is energizing the rotary magnet 326. Said magnet releases, which again closes the operating path for the top winding relay 32| and in turn closing ground to the rotary magnet 326. Thus the switch continues to step from left to right until the brush 3M which is now contacting with the top row of terminals in the bank 305, makes contact with terminal 333. Theninstead of relay 32| releasing as before, it remains operated over a circuit from ground on lead 3H! traced through lower winding relay 32|, bottom inner contact and armature relay 3|6, conductor 322, contact 323 .on relay 3| lower winding relay 324, thence over lead 325 and brush 30| to battery'on terminal 333, as previously traced through right winding relay 222 in station B line circuit. The current thus flowing is sufiicient tooperate relay 324 but is not sufiicient to operate relay 222.

Relay 324 in operating, at its top inner armature and contact, first closes a holding circuit for itself over lead 331 and upper frontv contact relay 3|6, conductor. 336, and contact 335 to ground. Relay 324 at its outer upper armature and front contact closes a circuit for operating relay 3 and at its outer upper armature and back contact opens the circuit of the releasemagnets as will later be described. Relay 324 at its lower innermost contact and armature completes a path which shunts out the previously traced path through contact 323 on relay 3 and lower winding relay 324, thereby reducing the circuit resistance and permitting relay 222 of Fig. 2 to operate and remove ground for starting other line finders.

Going back to the closure of a circuit on relay 324 for operating relay 3, this path is traced from ground on top spring of line finder V. O. N. springs over conductor 336, outer upper armature and front contact of relay 324, direct to battery through top winding relay 3. Relay 3 operating at its upper armature and contact opens the battery supply for vertical magnet 3l9 and for upper winding relay 32|. Relay 32| however, continues to hold on its lower wind- Relay 3| in operating at contact 3|4 opens the circuit to relay 3|6 previously traced over conductor 3|5 causing it and relay 32| to release. Release of relay 3|6 opens at its upper front contact a holding circuit for relay 324 but the latter does not release due to brush 34! of the rotary selector of Fig. 3A having taken one step into the grounded bank 342 as will later be described. A holding circuit for relay 324 may, therefore, be traced from ground in bank 342 over brush 34!, conductors 343, 344 and 345 to inner'upper armature and front contact relay 324, through top winding relay. 324 to battery. In this manner relay 324 remains operated until the signal interrupter of Fig. 4 has completed sending back the necessary signals for identifying the called station line B as will later be described.

The principal function of relay 3 operating as described above is to extend at contact 365 the start wire circuit to the next idle available line finder circuit so that other called lines may be identified during the sending back of signals on the first call previously traced. For example, a second line in subgroup 10 being called at this time would again operate relay 4l0 which at its upper contact would connect groundon conductor M6 to conductor 4", thence through contact 365 on relay 3| I, conductor 366, bottom contact relay 3l2, conductor 36'! to armature 421 on relay 4 of the next finder ILFIUA if it were idle, or to the next finder circuit that is idle.

Movement of rotary selector and transmission of identification signals The operation of relay 324 at its bottom contact connects battery to conductor 33B thence through rotary magnet 339 to ground on bottom contact of selector off-normal springs 340. The rotary magnet 339 operates and the rotary selector switch of Fig. 3A takes one step and causes off-normal springs 340 to operate. The circuit including rotary magnet 339 is thereby extended over conductor 368 to cam ST on signal interrupter as shown in Fig. 4 and thence to ground at feed cam FD during the time the live segment on cam ST is passing under its brush. Since the signal interrupter,is rotating continuously it will be observed that one live segment passes under its brush once every revolution of the interrupter and in this manner the rotary selector in Fig. 3A will be stepped one step ahead for every revolution of the interrupter. It will, therefore, be apparent that the selector brushes 34| and 369 remain on each terminal of the selector banks 342 and 346, respectively for the duration of one revolution of the signal interrupter.

Transmission of impulses corresponding to code number called station When rotary selector of Fig. 3A is stepped off-normal, brush 369 comes to rest on the first terminal which in this case is blank and has no function in sending back signals because the length of time it remains on this terminal is variable depending on the position of the live segment on cam ST when the selector takes its first step. When cam ST passes under brush connected to conductor 368 the selector will step to the second terminal and from now will remain on each terminal one full revolution of the interrupter. The second terminal in bank 346 is connected to the conductor 341 which contacts with cam marked FIG on signal interrupter of Fig. 4. The cutting of this cam gives out a signal which when it is received at the calling station A printer causes the receiver to shift to the upper case position ready for printing fig-' ures. The circuit over which'the signal reaches the calling station A is traced from positive battery on feed cam FD, over cam shaft 4| 8, live segments on cam FIG, thence over conductor 34'! to' brush 369 of Fig. 3, conductor 348, contact 349 on operated relay 324, conductor 350 and selector brush 302 to terminal 351 on which the line finder-is resting; thence over conductor 352, contact 224 on cutofl5 relay 220 of Fig. 2, portion of tip conductor 225, and right front contact on operated relay 222, tip conductor2l5, terminal and brush 226 of regular connector switch, top winding relay 209 to positive grounded battery 2l2 on back contact relay 208. Positive battery interruptions over the circuit thus traced, therefore, causes the operation and'release of relay 209 which at its top armature and contacts repeat the signal into the called subscribers loop over the conductors-205 and 206 all in a manner commonly found in telegraph repeater systems. This operation may be explained by pointing out that the current inthe lower winding of relay 209 tends to hold the armature to its-front contact but the line current in the upper winding thereof is twice as great and the relay therefore .is held to its back contact to cause current to flow in the calling station line A. The positive battery applied to the repeater by the signal interrupter shunts out the current in the upper winding of relay 209 to cause it to repeat open or no current signals to the calling station A.

' When signal interrupter of Fig.4 enters the period of its next revolution the segment on cam ST closes ground momentarily to the conductor 360 which is further traced through contact 353 on selector springs 340, through winding rotary magnet 339, conductor 33B, and battery through bottom contact and armature on relay 324. Thus the selector is caused to step to the third terminal where it .'remains until signal interrupter shaft 4|B makes another revolution; During this period selector brush 369 contacts with a terminal in" bank 346 which connects to conductor 354 for supplying a code positive battery interruption traced from cam FD, through signal interrupter shaft 4! cam I, conductors 449 and. 354, brush 369 and thence over same path as traced in previous paragraph. This positive battery signal is received on the calling subscriber station A printer .as the number 1 and identifies the particular' thousand in which the called line is located.

' When signal interrupter starts its next revolution the selector is caused to step tothe fourth terminal as above described where it remains during the remaining portion of this revolution. At this time the number 3 is printed at the calling station printer due to code positive battery interruptions traced from cam FD, through signal interrupter shaft 4l8, cam 3, conductors 420 and 355 to brush 369 and thence over a path previously traced. This positive battery ground signal identifies the particular hundred in which the called line is located. on the next or fifth terminal of the selector, the number 0 is transmitted by code positive battery interruptions traced from cam FD, through'signal interrupter shaft 4I8, cam 0, conductor 42], terminal 356 in finder bank 308, brush 304,'conductor 351to terminal in bank 346 of rotary selector, brush 369 and thence over same path as previously traced. This positive battery signal. identifies the particular group of ten in which the line is located. Similarly on the sixth terminal of the 7 interruptions are transmitted to subscriber station A printer through repeater relays 289 and 208 of connector circuit" CN indicated in Fig. 2 and serveto restore the printer tothe lower case position ready to receive and transmit the' message. The path for these ground interruptions is traced from ground at feed cam FD, through signal interrupter shaft 8, cam LTR to conductor 423 and associated terminal in selector bank 346, thence through brush 369' and over the same path previously traced for other signals. In this manner the number of the called line B is automatically recorded on the printer of the calling line A.

Release of ident iflcation line finder. V

' During the period in which the answer-back signals, arebeing' sent to the calling-station, the identification line finderILFlll is being held by ground at switch bank'342 over a path as previously described. When'therefore the circuit of the selector switch rotary magnet 339 is closed to step the switch to the eighthterminal, brush 3 in bank 342 inthis position of the selector no longer-is connected with ground so thatrelay 324 releases thereby closing a circuit for operating the release magnets of both the identification line" finderjand: the associated rotary selector; This circuit may be traced from ground at top contact 33501 line finder V. O. N. springs, con-' ductor 336, upper armature and back contact relay 7 3 I 6 to battery through upper winding relay 1 3| I for holding'the'latter relay during the release period; and to battery throughupper armature and back contact relay- 324, conductor 360,"upper armature and back contact relay M2, and conductor 36l,'thence' over th'e two release'magnet paths in parallel. The selector release magnet path is traced from conductor 36l, over lead 310, up'percontact and spring of selector off-normal J springs 340, and the finder release magnet path is traced from conductor 36l, over lead 3', and lower contact and lower spring on finderV. O. N.

springs; In thismanner bothof said switches are caused to restore to normal. The removal of ground from lead 336 at contact 335 of the V. O'. N. springs when the switch comes to normal,

opens the circuit for the release magnets and for relay 3. The latter relay normally releases and makes said line finder available to serve a succeeding call. 'If, however, some other identification line finder is' being started at this particularmoment, ground will be present on lead 4|! thus maintainingrelay 3 in an operated.

conditionthrough its lower winding .and conductors 364, 424 and 425 to battery. at back contact-andarmature of relay 426 at the bottom of Fig. 1. soon, however,"as the start wire is not 'beingfienergizedrelay 3lI-will release and the finder will be ready to serve another call. The

' connection between STA. A and STA; B of Figs. 1

and 2 in'the meantime remains and continues to function to transmit the subscribers messages in the usual manneniz Alarm and all finder busy Referring to Fig. 40 of Sheet 4, this circuit arrangement provides for giving an alarm in the event that all finders are busy. This is accom: plished by a normally closed circuit traced from battery through relay 428, conductor 429 to junc-l tion 430, thence through a normally made icontact onbottom of finder relay 3 and in par? allel with similar contacts on other finder relays suchas represented by relay 4, back to. junction 43l, conductor 432 to ground through the winding of relay 433. Both relays 428 and 433 therefore remain normally operated as, shown in V the drawings. If'all finders are busy relays 428 and 433 will release to operate relay M5 to thereby open the primary ground on. the start circuit.

1f the trouble ground still persists, the operation.

of relay H5 at its bot-tom contact removes'ground from the conductor 4l6.that connects to the start wire circuit. through the upper make contacts on relays 40! .to- 4I0 inclusive.

ms 'pere mits a finder relay 3 or 4 to release as soon as a finder circuit completes its function of sending answer-back signals and thereby permits the start wire circuit to functionagain in its normal way by reoperating relays 428 and .433. It, however; a trouble ground is present anywhere'on the start wire conductors 6,4, 434, 435, 436, 431 or'extension of same througlicontacts on relays 3H and4ll all finders will be started erroneously then said ground should be traceable eventually over lead 438, contact ,439 on relay M5 to battery through winding relay 440. (The latter relay operating under these conditions would operate relay 4 and in turnrelay'426. Relay 4 would also light trouble lamp 442 while operation of relay 426 wouldremove bat-1 tery from the holding windings of all finder relays 3H and 4Il.. This permits said -'relays to restore and the relays 428 and 433 to reoperate and release relays 440 and.426 but relay 44l :will,

remain locked to light lamp 442 until released 7 by momentary operation of key 444. If the trouble ground should clear :of, itself .in the mean time, relays M5 and 426 will have already been released to permit the start wire to again fun'c.-

tion. In the event a trouble battery is present anywhere on start wire conductors attaching to 'J'unction point 430, relay 428 would bemade to release while relay 433 remains operated. Under to inform thee-t this conditionlamp 443 lights tendant of 7 this condition.

What is claimed is;

1. A printing telegraph: system comprising a plurality of subscribers stations, a central office,- telegraph printer sets at said subscribers stations, means at each of said stations for initiating a connection between the printer set at the calling subscriber's station and a printer set at any one of the other of said subscribers stations,

automatically operated means at saidfcentral oflice for completing in response to the opera-, tion of said initiating means, said connection, identifying line-finder and a rotary stepping switch both responsive' to theestablishmentbf i said connection between the calling'andthe called subscribers stations, an impulse transmitter for numbers'of said stations, circuit means selec-. tively operative in response to theoperation of said identifying line-finder and said rotary stepping switch for causing to be repeatedto the calling subscriber's station the combination of transmitting combinations of groups of current,

impulses respectively, corresponding to the code 7 groups of current impulses corresponding to the code number of the connected called subscribers station.

2. A telegraph circuit, according to claim 1, wherein the line finder switch is an idle one of a group, any one of which, if idle, is accessible, upon the establishment of said connection, for selecting and then causing to be repeated to the calling subscribers printer set groups of current impulses corresponding to the code number of the connected called subscribers printer set.

3. A telegraph circuit, according to claim 1, wherein the line finder switch comprises four banks of contacts, one whereby the switch is maintained in an operated position while the groups of current impulses corresponding to the complete code number of the connected called subscribers printer set are being transmitted to the connected calling subscribers printer set; another whereby the line extending to the connected calling subscribers printer set is connected to the current impulse transmitter and over which the groups of current impulses respectively corresponding to the thousands and hundreds digit of the code number of the called subscribers printer set are transmitted to the calling subscribers printer set; another over which the group of current impulses corresponding to the tens digits of the code number of the called sub scribers printer set is transmitted to the calling subscribers printer set; and another over which the group of current impulses corresponding to the units digit of the code number of the called subscribers printer set is transmitted to the calling subscribers printer set.

4. A telegraph circuit, according to claim 1, wherein the rotary stepping switch comprises two banks of contacts, one for effecting the timing of transmission of the current impulse groups corresponding to the several integers in the code number of the called subscribers printer set, and the other for effecting when all the groups of current impulses corresponding to the complete code number of the called subscribers printer set has been transmitted, the release of the auxiliary line finder switch and the rotary stepping switch.

5. A telegraph exchange system comprising a plurality of subscribers stations, a central office, a circuit connecting each of said subscribers stations to said central ofiice, means at said central ofiice for automatically interconnecting in response to a call from any one of said subscribers stations, a plurality of said subscribers stations for communicating purposes, other means at said central ofiice for repeating back to a calling subscribers station the code number corresponding to the connected called subscribers station, said other means including an identifying circuit associated with the circuit of said called subscribers station, a plurality of continuously operating signal transmitting devices for respectively transmitting different groups of current impulses, a non-numerical selecting device for preparing said interconnected subscribers circuits for connection to said signal transmitting devices, a timing device for completing the connection of certain of said signal transmitting devices to said interconnected subscribers circuits in a desired sequence to correspond to the code number of said connected called subscribers station, and means responsive tothe operation of the identifying circuit associated with said called connected station for effecting the joint operation of said selecting and said timing device.

6. A telegraph exchange system, according to claim 5, wherein the non-numerical selecting device is a line finder switch of the step-by-step type and said timing device is a switch of the single-movement rotary type.

'7. A telegraph exchange system, according to claim 5, wherein said timing device comp-rises a circuit arrangement for restoring itself to normal after the last digit of the code number of the called subscribers station is transmitted to said calling subscribers line and for restoring to normal said non-numerical selecting device to permit direct communication between said calling subscribers line and said connected called subscribers line. I

8. A telegraph exchange system comprising a plurality of subscribers stations, a main station, printing telegraph equipment and a source of power therefor at each said subscribers station, said source being normally disconnected from its associated equipment, a normally open line circuit connecting each of said subscribers stations to said main station, switching means at each of said subscribers stations for closing its associated line circuit, pulsing means at each of said subscribers stations for transmitting an intermittent current over its associated line circuit, automatically operated means at said main station responsive first to said switching means and then to said pulsing means for interconnecting one of said subscribers stations with any other of said subscribers stations, means responsive to said automatically operated means for operatively connecting the power source of each of said subscribers stations operatively interconnected, to its associated printing equipment, line finding apparatus responsive when the first mentioned automatically operative means effects the interconnection of one of said subscribers stations and any other of said subscribers stations, a continuously operating device common to said plurality of subscribers stations for simultaneously generating groups of current impulses in various combinations, means for selecting the combination of impulses corresponding to the code number of said other of the subscribers stations, means for transmitting said selected combinations of impulses to said one of the subscribers stations whereby said one of the subscribers stations is assured of an established connection to the desired subscribers station, and means for restoring to normal the line finding apparatus operated in response to the establishment of said interconnection and said selecting means, as soon as a complete combination of groups of current impulses corresponding to the code number of said other subscribers station has been transmitted to said one subscribers station.

9. A telegraph exchange system, according to claim 8, wherein the line finding apparatus comprises a plurality of line finder switches, means for selecting an idle one of said line finder switches in response to the establishment of a connection between said one of subscribers stations and said other of said subscribers stations, and means for preparing another of said line finder switches for engagement by any other of said subscribers stations during the time that the selected line finder switch is engaged.

FULLERTON S. KINKEAD. 

